A unique tool, i.e., "VeriWeb", is employed to automatically discover and systematically explore Web-site execution paths that can be followed by a user in a Web application. Unlike traditional spiders (or crawlers) that are limited to the exploration of static links, VeriWeb can navigate automatically through dynamic components of Web sites, including form submissions and execution of client-side scripts. Whenever examining a new Web page, the system determines all possible actions a user might perform--be it a link, via a button with a JavaScript handler, or via form submission--and can execute them in a systematic way. In order to systematically test different paths in a Web site, VeriWeb addresses two critical problems: systematic Web site exploration and automatically filling out forms.